The cornea (the clear window at the front of the eye) would be completely spherical in an ideal world however the great majority of people have some degree of astigmatism where the cornea is more rugby ball shaped. If you imagine a magnifying glass which is rugby ball shaped you will appreciate that it would be hard to focus the light properly and get a clear image. This astigmatism of the cornea causes blur and is corrected by spectacles. This astigmatism has an effect on vision on top of any long or short sightedness you may have.
We do some calculations to work out what power of lens to put into the eye to try and take away any long or short sightedness but if you are left with astigmatism that will mean that your unaided vision (vision without spectacles on) can still be sub-optimal.
Because astigmatism involves the cornea being more curved in one axis than the other (rugby ball shape), incisions can be used in the more curved axis to reduce the astigmatism so the cornea has a rounder shape (football). The procedure is called astigmatic keratotomy or AK and is available as an adjunct to your private cataract surgery. The aim is to make the cornea a better shape so that your vision without spectacles is better than it would be without addressing that.
I use a diamond blade to make specially placed incision in the cornea at the time of surgery. The placement and depth of the incisions is worked out using a special algorithm.
This technique can reduce a significant amount of astigmatism but the results can be variable as everyones cornea behaves differently.
Another alternative is to use a lens in the eye which counters the astigmatism of the cornea – a toric lens.